This application claims the priority of German application 198 49 051.8-15, filed in Germany on Oct. 24, 1998, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a starterxe2x80x94generator system which is to be arranged between an internal-combustion engine and a transmission, particularly applications in the motor vehicle field being provided for such starter generator systems.
In the case of motor vehicles according to the current state of the art, it is generally customary to use separate starter and generator assemblies in the form of a starter and a generator. Reasons concerning the drive, the installation space and the weight indicate that such a solution does not seem to make sense in the knowledge that electric machines which can be operated as a motor as well as a generator are known. However, the torque requirement for generating the electric energy, thus for the generator operation, is several times smaller than the maximally required starting torque, which is a situation which would require a machine which is overdimensioned for the generator operation, or other measures.
In connection with vehicle concepts which have recently received increased attention, additional demands are made on the function of the starting as well as on the function of the generating of electric energy. Thus, for example, a significantly larger number of starting events occurs in connection with vehicle concepts in which the internal-combustion engine is switched off in phases in which no drive is required, thus, for example, when stopping at a traffic light, during the so-called start-stop operation of vehicles. In addition to the much higher frequency of starting events in such an operation, this operation also has the result that the number of the xe2x80x9ccold starting eventsxe2x80x9d with a particularly high required starting torque in percent relative to the sum of all starting events is significantly lower than in the case of conventionally driven vehicles, and that such starts caused by interruptions of the operation also encounter particularly favorable starting conditions with respect to the engine temperature and therefore require a particularly low starting torque which, in comparison to the starting events which frequently occur in the all-day operation during the day and are caused by usage interruptions, is still lower.
In addition, the striving for an increasingly lower fuel consumption and for operating modes which are particularly favorable for the environment also leads to thoughts about changing the kinetic energy of the vehicle in the braking operation into useful energy, thus, utilizing it, for example, for generating electric energy.
When taking these aspects into account, the demand arises for a system which, while its basic construction is the same, permits the most varied operating modes and which, in addition to the usual requirements with respect to space, weight and costs, also supplies possibilities of an extensive standardization in order to reach the required piece number degression as the result of an application range which is as wide as possible.
In addition to the systems which are still customary today and are constructed of a generator and a starter, thus of separate individual assemblies, solutions are also already known which operate with integrated starterxe2x80x94generator units.
In the case of such a solution known from U.S. Patent Document U.S. Pat. No. 48 62 009, the starterxe2x80x94generator as a drive unit is arranged coaxial to the crankshaft and is in a direct driving connection therewith. In this case, the crankshaft is connected with the planet carrier of a planetary drive which is arranged in the transition from the crankshaft to the generator consisting of the case-fixed starter and the rotor situated coaxially to the crankshaft. The rotor shaft carries the sun gear of the planetary drive in a non-rotatable manner, whose planet gears meshing with the sun gear and the ring gear are situated in a plane which is in parallel to the plane of the planet carrier but axially offset in the direction of the generator.
The rotatable ring gear is to be connected with the planet carrier by way of a bridge and a clutch which acts between the bridge and the planet carrier and locks only in one direction, and the bridge situated in the transition of the ring gear and the planet carrier, in turn, must also be connected with the case by way of a clutch which locks only in one direction. In this case, the clutch between the case and the ring gear locks counterclockwise relative to the rotating direction of the ring gear; the clutch between the planet carrier and the ring gear, again relative to the rotating direction of the ring gear, locks clockwise. This permits a starter operation with a step-down gearing and a generator operation with a rotational speed of the rotor which corresponds to the rotational crankshaft speed of the internal-combustion engine. Additional operating modes do not exist.
Another known solution, which is limited in its operating modes to the starter and generator operation, is known from German Patent Document DE 41 12 215 C1, in which case the flywheel which is situated in the transition between the crankshaft and the clutch and which is non-rotatable with respect to the crankshaft forms the planet carrier, with respect to which the rotor of the electric machine which consists of the rotor and the generator and can be used as the generator and the starter, is disposed in a coaxially rotatable manner, when non-rotatably connected with the sun gear of the planetary drive, which meshes with the planet gears carried by the planet carrier, which planet gears, in turn, mesh in the starter operation with the ring gear which is non-rotatably supported with respect to the case but is axially displaceable. As a result, in the starter operation, beginning from the starter, a gearing down takes place with a corresponding torque increase. In the generator operation, the ring gear is disengaged from the planet gears as the result of the axial displacement, and the planet carrier is connected with respect to the rotor by way of a centrifugal clutch locking in the rotating direction of the planet carrier non-rotatably connected with the crankshaft. If the rotational crankshaft speed exceeds the rotational rotor speed and the planet gears are released by the disengagement of the ring gear, as a function of the rotational speed, by way of the centrifugal clutch, the rotor is interlocked with respect to the planet carrier. This solution also does not provide additional operating modes.
Furthermore, it is known (German Patent Document DE 196 45 943 A1) to arrange a starterxe2x80x94generator unit in the drive train between the engine and the transmission, and by means of the rotor of the starterxe2x80x94generator unit a centrifugal mass can be driven which is situated in the shaft train between the engine and the transmission and can be separated from the engine and the transmission in each case by way of a clutch. In the case of this solution, in addition to the so-called direct start, in which the electric machine, as the starter, is connected with the crankshaft of the internal-combustion engine, and the starter torque is decisive for the torque available on the crankshaft in the starter operation, a so-called impulse (inertial momentum) start can be carried out, at which first the centrifugal mass is separated by way of the addressed clutches from the internal-combustion engine and the transmission and is accelerated by way of the rotor of the electric machine, and in the case of which, after a defined rotational speed has been reached, the clutch situated between the centrifugal mass and the internal-combustion engine is engaged so that, by way of the rotational energy of the centrifugal mass, the internal-combustion engine can be started. The respective starting methodxe2x80x94direct start or impulse startxe2x80x94is selected as a function of the temperature of the internal-combustion engine. Although, in this known solution, the operating modes, in which the starterxe2x80x94generator unit can be driven, are expanded, specifically by the possibility of the impulse start, this takes place in connection with relatively large expenditures and with the elimination of the possibility of the direct start while raising the starter torque by a corresponding gearing.
An object of the invention is a starterxe2x80x94generator system which, while the basic mechanical construction is the same, in addition to the impulse start, permits a number of other operating modes by a different controlling of the locking devices.
The starting point in the case of the starterxe2x80x94generator system according to the invention is a planetary drive with assigned locking devices by way of which, corresponding to their respective control, the ring gear is to be locked with respect to the case in the sense of a case interlocking and/or the planetary drive is to be locked in itself in the sense of a planetary drive interlocking, in which case at least parts of the planetary drive can simultaneously be utilized for the impulse start as the centrifugal mass.
In a basic construction of such a starterxe2x80x94generator system, the starterxe2x80x94generator system, comprising the electric machine as well as the planetary drive, may preferably be arranged coaxially with respect to a shaft section which is situated in the shaft train forming the drive connection of the internal-combustion engine and the transmission and is non-rotatably connected with the crankshaft, but is separably connected with the manually shifted transmission by way of a driving clutch which can be operated by the driver or automatically, or in the case of automatic transmissions, with the transmission by way of clutch devices assigned thereto. The shaft section forms the bearing for the rotor of the electric machine as well as for the ring gear of the planetary drive whose planet carrier is non-rotatably connected with the shaft section.
In connection with a locking device in the form of a controllable clutch between the case and the ring gear and another locking device in the form of a controllable clutch between the ring gear and the planet carrier or between the ring gear and planetary gears, or between the ring gear and the sun gear, the preferred solution for such a planetary drive interlocking being the arrangement of the respective locking device between the ring gear and the planet carrier, in addition to the impulse start, various forms of the direct start and also different forms of the generator operation in the driving operation as well as in the recuperation operation are conceivable. Thus, it is possible, for example, to use for the impulse start only parts of the planetary drive in conjunction with the rotor as the centrifugal mass if first, for the mass acceleration, both locking devices are open and subsequently, virtually as a form of second starting phase, the case interlocking is closed, while the planetary train interlocking is open.
The planetary drive, as a whole, can be used together with the rotor as a centrifugal mass, if the impulse start is not, as described above, implemented in two but in three starting phases; specifically a first starting phase in which the planetary train interlocking and the case locking are open; a second starting phase in which the planetary train interlocking is closed and the planetary train as a whole together with the rotor forms a unit which is non-rotatable in itself, and the case interlocking is open; and in a third phase in which the planetary train interlocking is open and the case interlocking is closed. Thus the third starting phase offers the possibility for continuing, starting from an impulse start with a maximal flywheel utilization energy a starter operation in which the torque of the electric machine is correspondingly raised by the gearing-down by way of the planetary drive.
As in the case of the impulse start, in the case of the direct start, the work may take place with or without gearing, with gearing while the planetary train interlocking is open and the case interlocking is closed, without gearing when the planetary train interlocking is closed and the case train interlocking is open. Analogously to the starting operation, the generator operation is conceivable at a rotational speed corresponding to the rotational speed of the internal-combustion engine or at a rotational generator speed which is raised in comparison to the rotational speed of the internal-combustion engine in the cases of a corresponding gearing of the planetary drive. This can take into account the normal situations in the driving operation in which, at high rotational speeds of the internal-combustion engine, the generator output is normally above the requirements, but at low rotational speeds of the internal-combustion engine, it does not meet the requirements. For a generator operation at a rotational speed corresponding to the rotational speed of the internal-combustion engine, the planetary train interlocking is closed but the case interlocking is kept open; for a generator operation at a rotational generator speed raised with respect to the rotational speed of the internal-combustion engine, the planetary train interlocking is open and the case interlocking is closed.
Furthermore, the further development of a starterxe2x80x94generator system according to the invention also permits the recuperation operation, in which the full utilization of the respective possibility is, however, possible only in conjunction with an additional clutch in the transition from the shaft section carrying the starterxe2x80x94generator unit to the crankshaft of the internal-combustion engine, because then it is possible, for example, in the braking operation, to operate the generator while the internal-combustion engine is uncoupled from the direction of the output side at a rotational speed which is higher than the rotational speed of the internal-combustion engine. If no clutch is provided between the starterxe2x80x94generator unit and the crankshaft of the internal-combustion engine, the rotational driving speed is limited also in the recuperation operation to the rotational speed of the internal-combustion engine or to the rotational speed of the rotor which, while taking into account the gearing ratios in the planetary drive, follows from the rotational speed of the internal-combustion engine.
In a further development of the invention, it is conceivable to longitudinally divide the shaft section which is in a non-rotatable connection with the starterxe2x80x94generator unit, such that, on the transmission side, this shaft section is formed by a shaft piece which is non-rotatably assigned to the ring gear of the planet carrier. Such a further development offers additional variation possibilities and also permits, despite the connection of the ring gear with the transmission input shaft, during the starting phase by the interlocking of the ring gear against the case, a separation of the electric machine from the transmission, and thus the elimination of the transmission drag moment in the starting operation.